Flavors and fragrances, but also insect attractants or repellents, are volatile molecules that can only be perceived over a limited period of time.
The perfume industry has a particular interest for compositions or additives which are capable of prolonging or enhancing the perfuming effect of a mixture of several fragrances at the same time over a certain period of time. It is particularly desirable to obtain long-lasting properties for standard perfumery raw materials which are too volatile or have a poor substantivity by themselves, or which are only deposited in a small amount onto the surface of the final application. Furthermore, some of the perfumery ingredients, especially aldehydes, are unstable and need to be protected against slow degradation prior to their use. Long-lasting perfumes are desirable for various applications, as for example fine or functional perfumery or cosmetic preparations. The washing and softening of textiles is a particular field in which there is a constant quest to enable the effect of active substances, in particular perfumes, to be effective for a certain period of time after washing, softening and drying. Indeed, many substances having odors which are particularly suitable for this type of application are known to lack tenacity on laundry, or do not remain on the laundry when rinsed, with the result that their perfuming effect is experienced only briefly and not very intensely. Given the importance of this type of application in the perfume industry, research in this field has been sustained, in particular with the aim of finding new, and more effective solutions to the aforementioned problems.
A variety of precursor compounds which release active material by a chemical reaction during or after application (using O2, light, enzymes, water (pH) or temperature as the release trigger) have been described as an alternative to encapsulation systems. In general, due to their inherent instability, the precursors often decompose in the application base during storage and thus release their fragrance raw material before the desired use.
In WO 95/16660, WO 97/34986, WO 98/06803 and EP 1 285 906, for example, acyclic acetals or related structures, which are capable of releasing mixtures of fragrance alcohols and aldehydes, have been reported. Said derivatives require hydrolytic conditions. From these systems, the fragrances are released as a pre-defined stoichiometric mixture of alcohols and aldehydes in a ratio of 2:1. This pre-defined mixture is not necessarily the ratio in which, for hedonic reasons, a person skilled in the art would like these compounds to be delivered. Furthermore, linear acetals and ketals are often quite unstable in a water-based environment, and therefore they are (at least in part) prematurely hydrolysed in water-containing consumer articles. On the other hand, cyclic acetals or ketals, as well as some related structures, such as those reported in DE 197 18 537, WO 00/04009, WO 00/38616, WO 2008/011742 or IN 2009DE00656 are often too stable to be efficiently used under mild application conditions because they typically require relatively harsh hydrolytic conditions and/or heating to be cleaved.
Stable acetals or ketals that could release fragrance aldehydes or ketones under mild reaction conditions by a trigger that is not based on hydrolysis would be advantageous for practical applications. In particular, the use of (natural) daylight as the trigger would be particularly suitable for the targeted use in perfumed consumer articles. The conjugates could easily be stored using opaque packing materials and, once deposited on the target surface and exposed to ambient daylight, slowly release the active compounds by light-induced covalent bond cleavage.
EP 1 262 473 reports 1-phenyl-2,2-bisalkoxy-ethanones as light sensitive precursors for the release of fragrance aldehydes and ketones. The light-induced cleavage of the precursor generates a pre-defined mixture of different fragrance compounds. Furthermore, the reaction mechanism involved in the cleavage of the conjugates gives rise to a series of different side-products which, from an application point of view might not be suitable.
Org. Lett., 2007, 9, 1533-1535, 1 Org. Chem., 2008, 73, 6152-6157 and J. Org. Chem., 2011, 76, 2040-2048 describe a photolabile cleavage approach for carbonyl groups protected as acetals or ketals based on 5-methoxysalicilic alcohol. The photodeprotection is preferably conducted in the presence of water. In Eur. J. Org. Chem., 2009, 2055-2058, Wang and co-workers describe the light-controlled release of anticancer agents; however, these compounds are very hydrophilic and non-volatile. Furthermore, they are released into an aqueous environment and not meant to be deposited and evaporated from a surface to impart their benefits.
We have now surprisingly found that the photosensitive acetal and ketal compounds according to the present invention solve the above-mentioned problems and are capable of efficiently liberating active volatile carbonyl compounds upon exposure to light in numerous practical applications. To the best of our knowledge, none of the above documents suggests, or allows to expect, that the photosensitive acetal and ketal compounds of formula (I) could indeed be suitable as delivery systems for the controlled release of volatile compounds.